A model of leishmanial infection (L. tropica) in the foot pad of in-bred mice has been found to be reproducible and useful for immunological and chemotherapeutic studies. Metastatic spread of the infection could not be attributed to impairment of the immune system as assessed by hemolytic plaque formation, and was not enhanced by an anti-B cell serum. The availability of different strains of leishmania that produce a spectrum of responses in the mouse model and cryopreservation techniques for maintenance of strains will permit comparative studies with this system. The amastigote-trypomastigote antigen prepared from cell cultures infected with T. cruzi was studied by gel diffusion procedures. The results by counter-immuno electrophoresis parallel very closely those obtained in complement-fixation tests. In those instances where specificity of reactions is in doubt, sera are examined by a variety of tests including IFA. Cell cultures are also being used to assess the infectivity of different strains of T. cruzi. These tests can be applied to organisms directly from infected triatomine bugs.